This invention relates to hypodermic syringes, and more specifically to a hypodermic syringe body adapted for delivering viscous liquids from prefilled cartridge-cannula units.
Bovine somatotropin (BST) is under development by several companies as an agent for increasing milk production efficiency of dairy cows. A particularly good vehicle for delivery of BST is the injectable sustained release formulation disclosed in U.S. patent application Ser. No. 06/768,605. The formulation is a viscous liquid comprising BST suspended in a carrier comprising from about 1% to about 20% wax and from about 80% to about 99% of oil. The present invention arose from the need to provide a reliable and convenient system for administering this formulation.
To minimize the risk of cross contamination between animals, an administration system utilizing disposable prefilled cartridges with attached cannulas was desired. A problem arose with existing technology in that there was a tendency to excess breakage of cannulas from the cartridges. Excess splitting of the cartridges was also experienced. These problems arose due to the viscous character of the formulation, requiring that a great deal of pressure be put on the syringe's plunger to administer the drug. The fact that the drug must be refrigerated between the point of manufacture and the point of use exacerbates this problem.